1. Field of the Invention
The present invention relates to exchanging routing information across a border between two autonomous systems using different routing protocols for packet switched networks.
2. Description of the Related Art
Networks of general purpose computer systems and specialized devices connected by external communication links are well known and widely used in commerce. The networks often include one or more network devices that facilitate the passage of information between the computer systems and devices. A network node is a network device or computer or specialized device connected by the communication links. An end node is a node that is configured to originate or terminate communications over the network. An intermediate network node facilitates the passage of data between end nodes.
Communications between nodes are typically effected by exchanging discrete packets of data. Information is exchanged within data packets according to one or more of many well known, new or still developing protocols. In this context, a protocol consists of a set of rules defining how the nodes interact with each other based on information sent over the communication links.
A link-state protocol is an example of a routing protocol, which only exchanges control plane messages used for routing data packets sent in a different routed protocol (e.g., the Internet Protocol, IP). To reduce the consumption of network resources and improve scalability, some routing protocols divide a large network up into smaller subnetworks. For example, the Open System Interconnection (OSI) protocol suite and the Open Shortest Path First (OSPF) routing protocol divide a network into domains and areas. A domain is a portion of a network under the network administration of a single authority, such as an enterprise or Internet service provider (ISP). A domain is also called an autonomous system (AS).
In an internetwork, networks in different autonomous systems (AS) also route data packets among each other. Routing information for an AS is summarized at its boundaries with one or more other ASs at intermediate network nodes called border gateway nodes or border gateway routers (BR).
When an AS border gateway router (ASBR) generate messages to internally advertise external routes it learns from an adjacent AS, it currently is able to set a forwarding address (FA) field in the message. The forwarding address is typically set for multi-access links between different AS, where by definition there can be more than one router of the same AS connected to the link with the different AS. Using the address in the FA field, other routers in the AS can determine when there is a better route to the different AS than through the ASBR. Use of the better route avoids performing one or more extra hops, and is called optimal routing herein.
The Internet Protocol (IP) is a routed protocol that assigns logical addresses to network nodes, which are easily nested in subnetworks of contiguous addresses that is advantageous for routing. IP version 4 (IPv4) addresses are the most widely used and are represented by four octets of binary digits (bits); each octet is 8 bits that represent decimal values from 0 through 255. Thus an IPv4 address has 32 bits. IPv4 supports 232 (about 4.3 billion) addresses, which is inadequate for giving even one address to every living person, much less for supporting a separate address for each connected device. IP version 6 (IPv6) has been introduced with 128-bit addresses in part to eliminate this problem.
Some routing protocols, such as OSPFv3, have been enhanced to use the IPv6 addresses. However, when the border router (BR) on the different AS does not have a global IP address, the forwarding address can not be utilized by current IPv6 routing protocols; and optimal routing is not available.